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Author: Floyd L. DavidsonFloyd L. Davidson Date: Aug 20, 2007 05:55
>On Sun, 19 Aug 2007 23:26:16 -0700, dplatt@ radagast.org (Dave Platt)
>wrote:
> >>"Digital" and "subject to aliasing" are two different things.
>>
>>As I believe the term "digital" is usually meant, it implies a
>>two-state (on/off) storage representation. It's not just that the
That describes a binary digital system. Not all digital systems
are binary. What is called M-ary is very common, with multiple
states.
>>signal amplitude is quantized, but that the quantization uses a
>>power-of-two representation and storage system of some sort.
It doesn't require a power of two representation, though that
certainly makes a lot of other functionality much easier. The
key is "discrete states" from a "finite set". That makes it
digital.
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Author: Floyd L. DavidsonFloyd L. Davidson Date: Aug 20, 2007 05:57
Jerry Avins ieee.org> wrote:>I like your categories. It is possible in concept to
>have a signal that is quantized in magnitude and
>continuous in time, but (unless we resort to counting
>electrons) I don't think it's possible in practice.
If you quantize the magnitude, it is digital. That is
by definition.
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Author: Don PearceDon Pearce Date: Aug 20, 2007 06:08
On Mon, 20 Aug 2007 04:57:03 -0800, floyd@ apaflo.com (Floyd L.
Davidson) wrote:
>Jerry Avins ieee.org> wrote:>>I like your categories. It is possible in concept to
>>have a signal that is quantized in magnitude and
>>continuous in time, but (unless we resort to counting
>>electrons) I don't think it's possible in practice.
>
>If you quantize the magnitude, it is digital. That is
>by definition.
No it isn't. It isn't digital until you assign numerical values to
those quantized levels. Until then it is simply a quantized analogue
signal.
d
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Author: AndorAndor Date: Aug 20, 2007 06:40
On 20 Aug., 10:04, nos...@ nospam.com (Don Pearce) wrote: > On Mon, 20 Aug 2007 03:51:54 -0400, Jerry Avins ieee.org> wrote:>>Don Pearce wrote:
>>> On Sun, 19 Aug 2007 23:26:16 -0700, dpl...@ radagast.org (Dave Platt)
>>> wrote: >
>>>> "Digital" and "subject to aliasing" are two different things.
>
>>>> As I believe the term "digital" is usually meant, it implies a
>>>> two-state (on/off) storage representation. It's not just that the
>>>> signal amplitude is quantized, but that the quantization uses a
>>>> power-of-two representation and storage system of some sort.
>
>>> My reading of the possible systems goes like this.
>
>>> analogue - a continuous representation of the original signal
>>> sampled - a representation of the signal at discrete time points
>>> quantized - a sampled signal, but with the possible levels constrained
>>> to a limited set of values
>>> digital - a quantized signal, with the individual levels represented ...
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Author: Floyd L. DavidsonFloyd L. Davidson Date: Aug 20, 2007 06:46
>On Mon, 20 Aug 2007 04:57:03 -0800, floyd@ apaflo.com (Floyd L.
>Davidson) wrote:
> >>Jerry Avins ieee.org> wrote:>>>I like your categories. It is possible in concept to
>>>have a signal that is quantized in magnitude and
>>>continuous in time, but (unless we resort to counting
>>>electrons) I don't think it's possible in practice.
>>
>>If you quantize the magnitude, it is digital. That is
>>by definition.
>
>No it isn't. It isn't digital until you assign numerical values to
>those quantized levels. Until then it is simply a quantized analogue
>signal.
If you quantize it, you *have* assigned a value to it,
and that value is not from a continuous set, but from a
discrete finite set, and therefore it is digital.
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Author: Don PearceDon Pearce Date: Aug 20, 2007 06:56
On Mon, 20 Aug 2007 05:46:19 -0800, floyd@ apaflo.com (Floyd L.
Davidson) wrote:
>>On Mon, 20 Aug 2007 04:57:03 -0800, floyd@ apaflo.com (Floyd L.
>>Davidson) wrote:
>> >>>Jerry Avins ieee.org> wrote:>>>>I like your categories. It is possible...
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Author: Don Stauffer in MinnesotaDon Stauffer in Minnesota Date: Aug 20, 2007 06:57
On Aug 19, 4:01 pm, Radium gmail.com> wrote:
>
> Is it true that unlike the-frequency-of-audio, the-frequency-of-video
> has two components -- temporal and spatial?
>
Kind of. This gets into some pretty involved engineering and math and
was originally used to get into how to analyze images when designers
were first trying to develop television systems. It involves what is
known as linear systems analysis, which originally was for one
dimensional signals such as audio. In this type of analysis any
arbitrary shape/waveform can be broken down into a collection of many
sine waves of different frequency. For images this was extended to
work as a two-dimensional array, with duplication of the signal by
considering two sets of so-called "spatial frequencies", at right
angles to each other.
This was extended beyond TV engineering when optical engineers
developed the Modulation Transfer Function by borrowing EE ideas of
linear systems to predict and measure performance of optical systems.
It involves things like Fourier transforms.
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Author: Doug McDonaldDoug McDonald Date: Aug 20, 2007 07:02
Radium wrote:
> On Aug 19, 2:50 pm, rfisc...@ sonic.net (Ray Fischer) wrote:
> >> Radium gmail.com> wrote:>
>>> Hi:
>
>>> I. Audio vs. Video
>
>>> Digitized (mono) audio has a single sample per each sampling
>>> interval.
>
Well, yes and no. That's true for what is called PCM, used
on the Compact Disc and MPEG. It is sort of true for Delta-Sigma
coding, but the for the actual useful sampling rate limit, its
not really true. D-S modulation is used for the Super Audio CD.
>
> There is no analog-equivalent of sample-rate? Then what the limits the
> highest frequency an analog audio device can encode?
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Author: Arny KruegerArny Krueger Date: Aug 20, 2007 07:58
> On Aug 19, 8:54 pm, dpl...@ radagast.org (Dave Platt) wrote: >> And, in fact, this concept of moving electrical charges is the basis
>> for one type of analog signal storage and playback device which has no
>> moving (mechanical) parts... the CCD, or Charge Coupled Device. It
>> consists of a large number of charge storage devices (typically MOSFET
>> transistors with dielectrically-isolated gates) hooked up as a sort of
>> shift register or "bucket brigade". Each gate stores a charge which
>> is proportional to the input signal present at a given moment in time.
>> Several thousand times per second, a clock pulse causes each storage
>> cell to generate an output voltage proportional to the charge in its
>> storage gate, and then to "capture" onto its gate the signal being
>> presented by the previous gate in the chain.
Thus introducing an important concept - sampled, non-digital signals.
Sampling and digitizing are somewhat independent. The necessary connection
comes when you realize that you have to sample something to digitize it.
OTOH, you don't have to digitize it when you sample it.
> Is CCD a form of analog non-volatile RAM?
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Author: Jerry AvinsJerry Avins Date: Aug 20, 2007 08:15
Floyd L. Davidson wrote:
> Jerry Avins ieee.org> wrote:>> Dave Platt wrote:
>>>> I'm curious to why there are no purely-analog devices which can
>>>> record, store, and playback electric audio signals [AC currents at
> ...
>
>>> The net result is that an audio CCD is capable of
>>> storing a
>>> decent-quality signal for only a few tens or hundreds of milliseconds,
>>> from input to output.
>>> Another sort of a purely analog signal-storage device,
>>> with no moving
>>> parts other than the electrons which convey the signal, is a simple
>>> length of transmission line (with perhaps some amplifiers mid-way).
>
> ... ...
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